function C1(name) {
  if (name) this.name = name;
}

function C2(name) {
  this.name = name;
}

function C3(name) {
  this.name = name || 'fe';
}
C1.prototype.name = "yideng";
C2.prototype.name = "lao";
C3.prototype.name = "yuan";
console.log((new C1().name) + (new C2().name) + (new C3().name));